1. Field of the Invention
The present invention relates to an inkjet recording head, which is capable of incorporation into information equipment such as a word processor, facsimile, and printer, a method for manufacturing the same, and an inkjet recording device. In particular, the present invention relates to an inkjet recording head configured to allow high-density arrangement in a two-dimensional array of piezoelectric elements and facilitate mass hie production thereof, a method for manufacturing such an inkjet recording head, and an inkjet recording device having such an inkjet recording head.
2. Description of the Related Art
In recent years, an impact recording process has attracted much attention for its small noise in recording and a high recording speed thereof. Among other impact recording processes, an inkjet recording process used in inkjet printers has been in wide use. The inkjet printer allows ink droplets to be ejected from the recording head and attached onto recording paper so that characters, figures and photographs are printed at a high speed. The inkjet printer is capable of recording the images onto plain paper without using a special fixation processing. According to a known inkjet recording process called drop-on-demand inkjet recording scheme, an electromechanical transducer such as a piezoelectric actuator is used to generate pressure waves (acoustic waves) in pressure chambers filled with ink, thereby allowing ink droplets to be ejected from the nozzles disposed in communication with the pressure chambers.
An inkjet recording head using the drop-on-demand inkjet scheme is described in JP Patent Publication No. Sho 56-64877. FIGS. 1A to 1C show the conventional inkjet recording head described in the publication. FIG. 1A is a longitudinal sectional view of the essential parts of the inkjet recording head, FIG. 1B a partially-broken top plan view thereof, and FIG. 1C a sectional view taken along the line cxe2x80x94c of FIG. 1B.
The inkjet recording head described in the publication has a base plate 44 and a diaphragm 42 which are coupled together to form a plurality of pressure chambers 45 therebetween. An ink nozzle, or orifice 43, is formed at one end of each pressure chamber 45. A plurality of rectangular piezoelectric elements 41 are mounted on the diaphragm 42 corresponding to the respective pressure chambers 45 The piezoelectric elements 41 are electrically connected to a pulse generator 40. The pressure chamber 45 is supplied with ink from an ink reservoir 47 through an ink supply tube 46. The piezoelectric elements 41 are made of piezoelectric ceramic, and more particularly, PZT (lead zirconate titanate).
In the conventional inkjet recording head as described above, the piezoelectric elements 41 are manufactured by machining a piezoelectric ceramic plate to configure predetermined size and shape. Examples of he method for machining the piezoelectric elements 41 with high precision include a dicing saw technique such as for cutting or trenching by using the rotation of a disc containing diamond particles (dicing blade), and a wire saw technique. These high-precision machining methods for piezoelectric elements, although suited to linear machining, are incapable of working the piezoelectric ceramic plate (piezoelectric plate) into arbitrary shapes.
An example of a manufacturing method for forming a piezoelectric plate into an arbitrary shape is described in JP Patent Laid-Open Publication No. Hei 11-207970. The manufacturing method described in this publication is as follows. Initially, a sheet of foaming agent is bonded onto a dummy glass plate, and a piezoelectric film is laminated thereon. A resist is applied thereon and patterned for mask portions. Thereafter, the piezoelectric film is subjected to cutting by sandblasting at regions other than those covered by the mask portions. Subsequently, the resist is removed. The resultant piezoelectric plates are subjected to positioning onto the ink reservoirs and placed on a conductive film formed on the diaphragm before the dummy glass plate is removed. Then, electrodes are mounted on the piezoelectric film to obtain the inkjet recording head. Using the manufacturing method described in the publication, the piezoelectric film can be formed into arbitrary shapes according to the mask pattern.
In the field of the inkjet recording heads, such an inkjet recording head having a two-dimensional array of a number of nozzles (hereinafter, this type of the inkjet recording head is referred to as a matrix head) is expected as the next-generation head in view of the high-density nozzle arrangement with suppressed increase in the head size. The technique described in the publication relates to an inkjet recording head having a plurality of piezoelectric elements arranged only in one dimension. It is silent as to the provision of a number of piezoelectric elements arranged in a two dimensional array at a high density to form a matrix head.
In view of the foregoing, it is an object of the present invention to provide a method for manufacturing an inkjet recording head by which a piezoelectric plate can be formed into arbitrary shapes and arranged at a high-density, i.e., in two-dimensional array of a number of piezoelectric elements as a matrix head, and which can be manufactured by simple manufacturing processes.
It is another object of the present invention to provide an inkjet recording head manufactured by such a manufacturing method, and an inkjet recording device incorporating such an inkjet recording head.
To achieve the foregoing objects, the present invention provides, in a first aspect thereof, a method for manufacturing an inkjet recording head which includes a two-dimensional array of a plurality of pressure chambers each communicating with a common ink reservoir, at least one diaphragm constituting part of walls of the pressure chambers, and a plurality of piezoelectric elements coupled to the diaphragm so as to correspond to the pressure chambers, the piezoelectric elements being activated to apply a pressure wave to ink in the pressure chambers so that ink droplets are ejected from nozzles which communicates with the respective pressure chambers.
A preferred embodiment of the method of the first aspect of the present invention includes the steps of: temporarily bonding a piezoelectric plate onto a substrate for allowing the substrate to be released from the piezoelectric plate; affixing a mask film onto the piezoelectric plate; patterning the mask film into a piezoelectric element mask pattern; subjecting the piezoelectric plate to sandblasting from above the piezoelectric element mask pattern to form a piezoelectric element array including a plurality of piezoelectric elements arranged in a two-dimensional array on the substrate; bonding the piezoelectric elements of the piezoelectric element array as a unit onto the diaphragm; and removing the substrate from the piezoelectric elements after the sandblasting.
The term xe2x80x9cpiezoelectric platexe2x80x9d as used in this text means a plate of a piezoelectric material such as a piezoelectric ceramic to be configured into a plurality of piezoelectric elements.
According to the method of the first aspect of the present invention, the piezoelectric plate can be cut into arbitrary shapes with ease to facilitate provision of a number of piezoelectric elements each releasable from the substrate. In addition, since the plurality of piezoelectric elements can be formed on the substrate as a piezoelectric element array having a two-dimensional arrangement, a high-density and two-dimensional array of a number of piezoelectric elements can be easily manufactured to form a matrix head.
The piezoelectric plate is preferably patterned by sandblasting. The patterning of the piezoelectric plate by using the sandblasting technique allows the piezoelectric elements to be formed on the diaphragm with ease irrespective of the number and arrangement of piezoelectric elements.
JP Patent Laid-Open Publications Nos. Hei 11-129476, 2001-88303, and 2000-79686 describe respective techniques for transferring a plurality of piezoelectric elements formed in block. However, all of these techniques are to form a plurality of piezoelectric elements on the substrate by using photolithography, screen printing, and the like, not the sandblasting. In contrast, according to the manufacturing method of the present invention, the plurality of piezoelectric elements formed on the substrate by patterning suing the sandblasting can be handled altogether as a unit of the piezoelectric elements. Consequently, despite the use of relatively inexpensive apparatuses, the step of forming a number of piezoelectric elements and the step of bonding the piezoelectric elements to the walls of the respective pressure chambers are both facilitated. Hence, the manufacturing method of the first aspect of the present invention simplifies the manufacturing processes and facilitates the mass production of matrix heads each having a number of piezoelectric elements arranged at a high density.
A method for manufacturing an inkjet recording head according to a second aspect of the present invention is applied to manufacturing an inkjet recording head of the type as described above.
A preferred embodiment of the method of the second aspect of the present invention includes the steps of: affixing a mask film onto a piezoelectric plate; forming the mask film into a pattern mask including a piezoelectric element mask pattern and a peripheral dummy mask pattern surrounding the piezoelectric element mask pattern; and applying sandblasting from above the pattern mask to pattern the piezoelectric plate based on the piezoelectric element mask pattern and the peripheral mask pattern.
The method for manufacturing an inkjet recording head in the second aspect of the present invention achieves effects similar to the effects of the method of the first aspect of the present invention. In addition, the peripheral dummy pattern formed in the peripheral area of the piezoelectric element array can suppress the side etching that occurs during the sandblasting, thereby assuring high dimensional uniformity of the piezoelectric elements.
More specifically, after the piezoelectric plate is subjected aid to sandblasting, the sandblast processing (etching) in the thickness-wise direction of the piezoelectric plate is accompanied by the processing in the width-wise direction of the piezoelectric plate, i.e., side etching. The side etching occurs due to the collision of blasting particles with the side surfaces of the piezoelectric plates in the sandblasting processing.
The rate of processing in the side etching in general depends on the widths of the processed trenches to be formed in the piezoelectric plate. That is, a larger width of the trenches to be formed along the piezoelectric elements increases the probability for blasting particles to collide with the sides of the piezoelectric plate. As a result, the side etching proceeds at a higher rate at the periphery. Due to this property of the sandblasting processing, the piezoelectric elements formed at the periphery of the piezoelectric element array suffer from higher side etching. That is, since the outer peripheries of the peripheral piezoelectric elements are not associated with the elements that protect the peripheral piezoelectric elements against the collision of blast particles onto the side surfaces, the side etching proceeds at a higher rate. As a result, the peripheral piezoelectric elements may be deteriorated in the dimensional accuracy. Since the sizes of the piezoelectric elements have a significant influence on the ejection characteristics such as droplet volume, droplet speed, etc., ununiform side etching among the piezoelectric elements as described above must be assured.
For this reason, in the method for manufacturing an inkjet recording head of the second aspect of the present invention, the peripheral dummy pattern is arranged so as to surround the piezoelectric element array. Consequently, the peripheral dummy pattern protects the peripheral piezoelectric elements against the side etching, thereby allowing the formation of a piezoelectric element array having high dimensional uniformity.
It is to be noted that JP Patent Laid-Open Publications Nos. Hei 9-39234, Hei 6-143563, and 2000-289200 describe techniques for forming dummy piezoelectric elements, which are irrelevant to the function of application of the pressure to the pressure chambers. The techniques described in these publications are, however, intended only to improve mechanical strength, wherein a base or the like mounting thereon the piezoelectric elements is coupled to the diaphragm. Thus, the foregoing advantages of the present invention such as xe2x80x9cfabricating well-cut piezoelectric elementsxe2x80x9d cannot be expected from them.
Prior to the step of affixing the mask film, the piezoelectric plate is preferably bonded onto the substrate for allowing the substrate to be released from the piezoelectric plate. The piezoelectric element array having a two-dimensional array of a plurality of piezoelectric elements arranged on the substrate is then formed, and the piezoelectric elements of the piezoelectric element array are bonded onto the diaphragm before the substrate is removed from the piezoelectric elements. In this step, the plurality of piezoelectric elements formed on the substrate by the sandblasting can be handled altogether as a unit. Consequently, the step of forming a number of piezoelectric elements and the step of bonding the piezoelectric elements onto the walls of the respective pressure chambers are both facilitated. Hence, the manufacturing method of the second aspect of the present invention simplifies the manufacturing processes and facilitates the mass production of matrix heads having a number of piezoelectric elements arranged at a higher density.
A method for manufacturing an inkjet recording head according to a third aspect of the present invention is applied to manufacturing the inkjet recording head as described above.
A preferred embodiment of the method of the third aspect of the present invention includes the steps of: affixing a mask film onto a piezoelectric plate; forming the mask film into a pattern mask including a plurality of piezoelectric element mask patterns and a dummy pattern disposed within a gap between each two column of the piezoelectric element mask patterns; and subjecting the piezoelectric plate to sandblasting from above the pattern mask.
In accordance with the method of the third aspect of the present invention, the dimensions of the piezoelectric elements have further improved uniformity by reducing the side etching effected at the respective sides of the piezoelectric elements.
In the third aspect, prior to the step of affixing the mask film, the piezoelectric plate is preferably bonded onto the substrate for allowing removal of the piezoelectric plate from the substrate.
In addition, the peripheral dummy pattern described in the manufacturing method according to the second aspect of the present invention may be used in the manufacturing method of the third aspect, in addition to the dummy pattern in the third aspect.
An inkjet recording head according to the present invention includes: a two-dimensional array of a plurality of pressure chambers each communicating with an ink reservoir; a diaphragm constituting part of walls of the pressure chambers; and a plurality of piezoelectric elements coupled to the diaphragm so as to correspond to the pressure chambers, the piezoelectric elements being activated to apply a pressure wave to ink in the pressure chambers so that ink droplets are ejected from nozzles communicating with the respective pressure chambers. In the structure, insulating resin films are formed on sides of the respective piezoelectric elements.
In the structure of the inkjet recording head according to the present invention, a two-dimensional array of piezoelectric elements arranged at high density is formed, with the insulating resin films formed on the sides of the piezoelectric elements. The insulating resin film protects the piezoelectric elements against a damage caused by dielectric breakdown of the piezoelectric elements which may occur due to absorption of moisture from the air, with an improvement in reliability.
In an inkjet recording head according to a first example of the present invention, the piezoelectric elements are arranged in a two-dimensional array on the diaphragm constituting the walls of the pressure chambers, with a peripheral dummy pattern being disposed around the piezoelectric elements.
According to the inkjet recording head of the first example of the present invention, the peripheral dummy pattern formed around the two-dimensional array of the piezoelectric elements is subjected to sandblasting thereby protecting the sides of the peripheral piezoelectric elements against the side etching. The piezoelectric elements have excellent uniformity of dimensions due to the function of the dummy pattern during the sandblasting.
In an inkjet recording head according to a second example of the present invention, intervening dummy patterns are disposed between each adjacent two of the piezoelectric elements.
According to the inkjet recording head of the second example of the present invention, all the piezoelectric elements in the piezoelectric element array are subjected to uniform side etching during the sandblasting step. Thus, the resultant piezoelectric elements have excellent uniformity in dimensions thereof due to the function of the intervening dummy pattern during the sandblasting.
In an inkjet recording head according to a third example of the present invention, the pressure chamber plate defining the pressure chambers has at least one positioning mark, the diaphragm has a through-hole positioned with respect to the positioning mark, and a piezoelectric plate on which the plurality of piezoelectric elements are formed has an alignment mark.
According to the inkjet recording head in the third example of the present invention, the pressure chambers and the piezoelectric elements can be aligned with each other with high accuracy by using the through-hole of the diaphragm.
An inkjet recording device according to the present invention includes any of the foregoing inkjet recording heads. It is possible to obtain an inkjet recording device which has piezoelectric elements of extremely high uniformity in shape, suppresses characteristic variances between ejectors, and is capable of outputting high-quality image signal.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.